1. Field of the Invention
This invention relates to a control apparatus of an internal combustion engine, and particularly to a control apparatus of an internal combustion engine for preventing trouble of a throttle valve of the internal combustion engine freezing up.
2. Description of the Related Art
In winter, trouble sometimes arises of dew condensing on the throttle valve of an internal combustion engine of an automotive vehicle and water droplets forming as a result of this dew condensation then freezing and the throttle valve freezing up. As processes by which this trouble of throttle valve freezing occurs, the following examples are known.
When an internal combustion engine is running, a flow of air in an intake pipe is constricted by a throttle valve. As a consequence of this flow of air being constricted by the throttle valve, the flow speed of the air in the intake pipe increases sharply in the vicinity of the throttle valve. Along with the increase in the flow speed, the air flowing through the vicinity of the throttle valve is sharply reduced in pressure, and the temperature of that air falls. In environments where the outside temperature is low, in places where the humidity is high such as on sea coasts and by rivers, when the internal combustion engine is operated from cold to warm, as a consequence of the reduction in pressure of the air in the vicinity of the throttle valve and the fall in air temperature, water vapor in the intake air condenses as dew on the throttle valve to form water droplets, and these water droplets freeze.
When the internal combustion engine is running, with the flow of air in the intake pipe being constricted by the throttle valve, the pressure in the intake pipe is reduced by the internal combustion engine, and when the internal combustion engine is stopped in this state, because the pressure in the intake pipe rises to atmospheric pressure, air flows into the intake pipe. When at this time the throttle valve is fully closed, a phenomenon of gas in the combustion chambers of the internal combustion engine flowing back into the intake pipe through the intake valves of the internal combustion engine occurs; in an internal combustion engine equipped with an exhaust recirculating device for recirculating exhaust gas into the intake pipe, a phenomenon of post-combustion gas in the combustion chambers flowing into the intake pipe through the exhaust recirculating device occurs; in a vehicle equipped with a positive crankcase ventilation device, a phenomenon of gas in the crankcase of the internal combustion engine flowing into the intake pipe through the positive crankcase ventilation device occurs; and in an internal combustion engine equipped with a fuel transpiration gas circulating device, a phenomenon of gas in the fuel tank flowing into the intake pipe through the fuel transpiration gas circulating device occurs.
Because these gases flowing into the intake pipe are all high-temperature, high-humidity gases, the intake pipe becomes filled with high-temperature, high-humidity gas. When in this state a throttle body incorporating the throttle valve is cooled by a low outside air temperature, the high-temperature, high-humidity gas in contact with the inner surface of the throttle body is cooled, water vapor in the gas condenses on the inner surface of the throttle body, and water droplets form. And also when high-temperature, high-humidity gas flows into a throttle body already cooled by low-temperature outside air, because this high-temperature, high-humidity gas makes contact with the inner surface of the cooled throttle body, the high-temperature, high-humidity gas is cooled, water vapor in the gas condenses on the inner surface of the throttle body, and water droplets form. And trouble arises of water droplets condensed on the inner surface of the throttle body collecting at the bottom of the throttle valve under gravity and surface tension and then freezing at the bottom of the throttle valve as the outside air temperature falls and causing the throttle valve to freeze up.
When this trouble of the throttle valve freezing occurs, as a result of the intake passage of the internal combustion engine being blocked, a situation in which good startability cannot be ensured when an attempt is made to start the internal combustion engine arises, and there is a risk of the vehicle becoming immobile.
Related art concerned with this problem includes JP-A-59-188050 (Related Art 1) and JP-A-2000-320348 (Related Art 2). In Related Art 1, in an apparatus in which while an internal combustion engine is running a target throttle aperture corresponding to the operating state of the engine is obtained and the aperture of a throttle valve is regulated to this target throttle aperture by means of an actuator, when the engine is operating in a low outside air temperature the throttle valve is oscillated in the vicinity of the target throttle aperture to remove water droplets condensed on the throttle valve and thereby prevent trouble of the throttle valve freezing.
In Related Art 2, in an apparatus in which while an internal combustion engine is running a target throttle aperture corresponding to the operating state of the engine is obtained and the aperture of a throttle valve is regulated to this target throttle aperture by means of an actuator, when the engine is started in a low outside air temperature, in a state before the internal combustion engine proceeds to full combustion, to prevent trouble of the throttle valve freezing, the throttle valve is made to oscillate greatly by the target throttle aperture being made to fluctuate greatly.
Related Art 1: JP-A-59-188050
Related Art 2: JP-A-2000-320348
However, in Related Art 1, although water droplets condensing as dew on the throttle valve while the engine is running can be removed, it is not possible to prevent dew condensation and freezing of water droplets forming as a result of this dew condensation after the-engine stops, and it is impossible to eliminate trouble of the throttle valve freezing after the internal combustion engine stops.
And, if condensed water droplets freeze 100% and the throttle valve reaches a throttle-frozen state, to oscillate the throttle valve to eliminate this throttle-frozen state a large shear torque is necessary, and with actuators normally used the situation often arises that the shear torque is insufficient and the freezing cannot be overcome. In Related Art 1, 2, because freezing of the throttle valve due to freezing of water droplets cannot be eliminated with certainty, the problem arises that sure startability cannot be guaranteed and it is difficult to prevent certainly a situation of the vehicle becoming immobile.
And, when a frozen throttle valve is oscillated forcefully, there is a risk of stress accompanying that oscillation causing damage to the throttle valve and its drive mechanism. And when an excessive current flows through a motor for driving the throttle valve, there is a risk of the drive motor burning out.